What is Arbovirus Encephalitides (arthropod-borne viruses)?
Arboviruses, also known as Arthropod-borne viruses, are a group of viruses carried and spread by insects like mosquitoes, ticks, or sandflies. These viruses come from several families: Togaviridae, Flaviviridae, Bunyaviridae, and Reoviridae. Uniquely, their genomes are similar in structure and consist of RNA, which allows them to mutate and adapt to different environments or hosts. For them to infect humans, they need these insect carriers, known as vectors.
It’s crucial to understand these viruses and the diseases they can cause as the occurrence of infections is increasing, and there’s a potential of new diseases emerging. Arboviruses can lead to several neurological diseases such as myelitis (spinal cord inflammation), neuritis (nerve inflammation), myositis (muscle inflammation), meningitis (inflammation of the membranes covering the brain and spinal cord), and encephalitis (brain inflammation). The probability of death increases if the person is diagnosed with encephalitis. Hence, arboviruses should always be considered when diagnosing a feverish patient showing neurological symptoms.
Although these viruses can cause a broad range of infections, this article will mainly focus on the major features of more common Arthropod-borne viruses that cause endemic (frequently found in a particular area) and travel-associated encephalitis.
What Causes Arbovirus Encephalitides (arthropod-borne viruses)?
The Chikungunya virus, part of the Togaviridae family, can be passed to humans through infected Aedes mosquitoes, through mother-to-child transmission, and through blood products. This virus can cause a disease known as chikungunya fever and in serious cases, it can cause meningoencephalitis, a condition that affects the brain and the membranes that surround it. These infections have mainly been reported in La Réunion Island and the Caribbean.
Eastern equine encephalitis (EEE) virus spreads through infected Culiseta melanura and some other types of mosquitoes. This virus tends to infect people more often in August and September, but it can occur at any time of the year. Among adults, about 2% develop diseases that affect the brain quickly, making EEE the most deadly of diseases spread by insect bites, with a death rate of at least 30%. No vaccines are currently available for humans, though a vaccine for horses exists.
Western equine encephalitis virus can be transferred to humans by infected Culex mosquitoes. It occurs in both North and South America, and it results in encephalitis in less than 1% of infected adults. Just like EEE, no vaccines are available for humans, but a vaccine is available for horses.
Venezuelan equine encephalitis (VEE) virus occurs in two forms: one spreads through many types of mosquitoes and the other spreads through Culex mosquitoes. The virus first results in fever-like symptoms, and it rarely leads to diseases that affect the nervous system. It has caused several outbreaks in North and South America.
Dengue virus, part of the Flaviviridae family, spreads through Aedes aegypti or Aedes albopictus mosquitoes. It can cause different levels of the dengue disease, ranging from mild to severe. Some studies found that these viruses can directly affect the brain and can lead to various forms of brain inflammation. The risk of having neurological symptoms varies from 0.5% to 21%. A vaccine is currently available in Latin America and Southeast Asia.
Japanese encephalitis virus (JEV) infects about 68,000 people each year in Asia where it is mainly spread by a specific type of Culex species. Out of all the people that contract the virus, less than 1% suffer from neurological diseases. Although the risk of infection for travelers is low, a vaccine is available in the US for people planning on visiting high-risk areas.
Murray valley encephalitis virus and St. Louis encephalitis virus are both transmitted by Culex mosquitoes. The first is found primarily in Australia, New Guinea, and Indonesia and causes symptoms similar to the flu, with a death rate between 15%-30% for severe infections. The second is important in the Americas and transmission mostly occurs in the summer when mosquitoes are active. This disease could cause neurological issues and has higher death rates in patients over 60 years old.
West Nile virus, Powassan virus, and tick-borne encephalitis virus are other mosquito and tick-borne infections. West Nile virus could be contracted via mosquito bites, organ transplantation, or blood transfusion. It mainly causes asymptomatic infections but may also lead to neurological diseases, with currently no available vaccines. Powassan virus is transferred by Ixodes ticks in the US and could cause neurological issues. Tick-borne encephalitis virus is transmitted by Ixodes ticks mostly in Europe and Russia and sometimes results in neurological symptoms in two stages, with vaccines available in Europe and Canada.
Zika virus, a mosquito-borne flavivirus, could be transmitted mainly by Aedes aegypti and could also transfer via maternal-fetal, sexual, blood products, organ transplantation, and laboratory exposures, causing multiple neurological complications.
The Bunyaviridae family includes the La Crosse encephalitis virus and the California encephalitis virus. The former is transferred by Aedes triseriatus mosquitoes and it’s the most harmful out of the California encephalitis group whereas the latter rarely causes central nervous system diseases and has a death rate of <1%.
The Colorado tick fever virus, part of the Reoviridae family, is transmitted via a Rocky Mountain wood tick and it’s limited geographically to the western U.S. and Canada. 5% to 10% of infected children could develop diseases affecting the nervous system but the death rate remains low.
Risk Factors and Frequency for Arbovirus Encephalitides (arthropod-borne viruses)
When determining the possible causes of encephalitis in a patient, several aspects should be considered. These include the patient’s exposure history, such as where they live, any recent travel, contact with insects or animals, their job, hobbies, and diet. All of these details can support the early stages of diagnosis. Other factors that could impact the diagnosis are the patient’s age, their vaccination records, immune status, and the time of the year. Also relevant is the information about what vectors and geographical areas are associated with each virus.
- Exposure history factors: place of residence, recent travel, insect contact, animal contact, occupation, recreational activities, and diet.
- Other important factors: age, vaccination history, immune status and seasonal variation.
- It’s also crucial to consider the vectors and geographical distribution related to each virus.
Signs and Symptoms of Arbovirus Encephalitides (arthropod-borne viruses)
Arbovirus infections cover a range of symptoms that are sometimes hard to pinpoint. People infected with it can have a wide variety of symptoms including fevers, headaches, changes in their mental state, seizures and specific neurological issues, often resembling those found in encephalitis. Some individuals might even feel like they have the flu before any of the neurological symptoms appear. Therefore, if a person experiences a combination of fever, headache, and changes in mental states, they could be showing signs of acute encephalitis syndrome, which is indicative of this infection.
Physical examinations can further help identify the cause of encephalitis. Skin rashes may point towards infections such as West Nile Virus (WNV) or Zika virus. Eye-related symptoms like inflammation in the back of the eye, bleeding in the retina, or vitreitis (inflammation of the jelly-like part of the eye) might suggest a WNV infection. Also, certain neurological signs can help understand the specific cause of viral encephalitis. For instance, specific arboviruses like WNV, St. Louis Encephalitis (SLE) virus, and Japanese Encephalitis Virus (JEV) can evoke symptoms related to Parkinson’s disease. These viruses can also trigger seizures, inflammation in the cerebellum, and symptoms of brain stem involvement.
Testing for Arbovirus Encephalitides (arthropod-borne viruses)
If a patient might be suffering from encephalitis, they might need a procedure called a lumbar puncture, provided it’s safe for them. During this test, cerebrospinal fluid (the fluid found in the brain and spine) will be collected and examined. Tests done on this fluid often show an increase in a type of white blood cell known as lymphocytes, normal sugar levels, and an increase in protein. The fluid will also be checked for bacteria with a gram stain test, which is usually negative in cases of encephalitis.
For further diagnosis, technicians might look for specific antibodies and use a technique called PCR to identify virus DNA in the cerebrospinal fluid and blood. However, sometimes there could be cross-reactivity among similar types of viruses, which is where a test called plaque reduction neutralization can help.
In addition to these tests, brain scans, especially magnetic resonance imaging (MRI), are usually considered to help identify encephalitis. MRI can reveal specific changes showing abnormal signal intensities and restriction of diffusion, which can be signs of a virus called West Nile Virus (WNV). Similar MRI changes have also been reported in other types of viral infections.
An electroencephalogram (EEG) is another test typically conducted. This captures the electrical activity of the brain and often shows general slow wave patterns in patients with viral encephalitis. In those with WNV, irregular slow waves are common.
If everything else doesn’t reveal the cause, a brain biopsy might be considered in people with worsening neurological symptoms to look for the cause of encephalitis.
Treatment Options for Arbovirus Encephalitides (arthropod-borne viruses)
If there’s suspicion or confirmation that a certain type of virus has invaded the nervous system, there are currently no specific antiviral treatments available to immediately cure the disease. The best approach to managing this condition is providing supportive care to the patient.
Protecting oneself from getting infected must be a priority, especially if you’re in an area known to have these virus-carriers. Some precautions to consider include controlling and reducing the vector (or carrier) population, using personal protective measures, and getting vaccinated if there’s one available in your area.
If you are planning to travel to a high-risk area, it’s crucial that you consider strategies to avoid infection. This could mean wearing long clothing to cover as much skin as possible, using insect repellents, and getting vaccinated for added protection, if a vaccine is available.
What else can Arbovirus Encephalitides (arthropod-borne viruses) be?
- Aseptic meningitis – a type of meningitis that is not caused by bacteria
- Autoimmune encephalitis – a condition where the body’s immune system attacks its own brain, causing swelling
- Bacterial meningitis – a serious infection of the brain and spinal cord’s protective membranes, caused by bacteria
- Herpes simplex virus (HSV) encephalitis – an inflammation of the brain caused by the herpes virus
- Tuberculous meningitis – a rare kind of meningitis caused by tuberculosis bacteria
- Fungal meningitis – a rare meningitis type caused by a fungal infection
- Brain abscess – a pocket of pus within the brain, typically caused by a bacterial infection
- Syphilis – a sexually transmitted infection that can affect the brain in late stages
- Malaria – a tropical disease spread by mosquitoes, which can affect the brain in severe cases
What to expect with Arbovirus Encephalitides (arthropod-borne viruses)
The outcome of a viral infection can differ for each virus. While most people who get infected do not show symptoms and fully recover, death rates can range from less than 1% to as high as 30% in cases where the virus invades the nervous system. Even those who recover from these severe neurological symptoms often have long-term nervous system complications.
Possible Complications When Diagnosed with Arbovirus Encephalitides (arthropod-borne viruses)
Many people who are diagnosed with encephalitis that’s transmitted by insects (arthropod-borne) often end up in the hospital to receive extra care, including assistance with breathing. It’s common for these individuals to face lasting impacts on their nervous system. For instance, research on patients who were hospitalized due to West Nile Virus encephalitis showed that they experienced issues with brain function and reported symptoms such as tiredness and other neurological symptoms. These symptoms could last from several months to several years after they first became ill.
Preventing Arbovirus Encephalitides (arthropod-borne viruses)
It’s crucial to be aware of diseases caused by arboviruses, which can be spread through mosquitoes or ticks. Since there is currently no treatment for these diseases, the best approach is prevention. This is especially important if you’re planning to travel to parts where these viruses are common. You can find out more about the areas with these viruses from resources like the Center for Disease Control (CDC) or the World Health Organization.
Using bug spray, wearing long sleeves, and checking yourself for ticks can significantly reduce the chances of you contracting these diseases. Hence, it’s essential to educate ourselves on these preventive measures when heading to endemic or disease-prone regions.
